The invention is related to a method for the determination of reduction parameters for the subsequent adjustment of a reduction device to reduce the fragments of a fractured bonee. The method comprises: measuring points on the surfaces of the corresponding bones of interest at the patient's left and right side of the body; establishing a plane of symmetry containing an anterior-posterior axis and a proximal-distal axis; generating a mirror image of the patient's non-fractured bone symmetrically to the plane of symmetry; and determining the reduction parameters by comparison of the coordinates of the points at the fractured bone with the coordinates of the points within the mirror image. The device according to the invention comprises: a cylindric or prismatic reference bar; clamps displaceable on and fastenable to the reference bar; screws or pins screwable into the bone transversely to the reference bar within the clamps; and an adjustable clamp to fasten a pin capable of being set with its tip to desired points on the surface of the bone.